Computershare 2018 report on Escheatment - https://content-assets.computershare.com/eh96rkuu9740/df5beb3a68bb4705b42ea612d31ca982/358538b031f683476ca1d4705bd0f8df/Escheatment_White_Paper.pdf
In the United States, generally, if an asset's owner is not able to be contacted and there knowledge of where they are, eventually assets will be turned over to the state after a due diligence period. Exact details vary by the state. Once at the state they can be claimed for a time by the individual or, in some cases, direct family.
In the case of stock, "Issuers and their transfer agents must conduct various due diligence mailings and database searches prior to the property being escheated, as required by the states or the Securities Exchange Commission (SEC)." See: https://www.law.cornell.edu/cfr/text/17/240.17Ad-17
WhyDRS should organize the escheatment protocols for each state and territory and provide this information to investors so that they are aware of what their home state rules are and how to avoid unintentional triggering of these policies.